The answer would be center of mass, B
We have that for the Question "A 2kg book is held against a vertical wall. The <em>coefficient </em>of friction is 0.45. What is the minimum force that must be applied on the <em>book</em>, perpendicular to the wall, to prevent the book from slipping down the wal" it can be said that the minimum force that must be applied on the <em>book is</em>
From the question we are told
A 2kg book is held against a vertical wall. The <em>coefficient </em>of friction is 0.45. What is the minimum force that must be applied on the <em>book</em>, perpendicular to the wall, to prevent the book from slipping down the wal
Generally the equation for the Force is mathematically given as

F=44N
Therefore
the minimum force that must be applied on the <em>book is</em>
F=44N
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Nitrogen
Explanation:
Adding one proton to a carbon atom makes Nitrogen.
A quick introspection on atoms:
- An atom is made up of three fundamental particles.
- They are protons, neutrons and electrons.
- The protons are positively charged and the neutrons do not carry any charges.
- Electrons are negatively charged.
The difference between an atom and another is the number of protons in them. This is the atomic number.
The periodic table of element is a list of elements arranged based on the number of protons they have. Every element on the table has unique number of protons which makes it differ from another.
- Atoms do not readily lose their protons because they are held by nuclear forces in the nucleus of an atom.
When an element gains a proton, it becomes another element.
Carbon has proton number of 6
If a proton is added to it, it becomes 7
This is the proton or atomic number of nitrogen.
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Acceleration a=3m/s^2
time t= 4.1seconds
Final velocity V= 55km/h
initial velocity U= ?
First convert V to m/s
36km/h=10m/s
55km/h= 55*10/36=15.28m/s
Using the formula V= U+at
U= V-at
U= 15.28-3*4.1=15.28-12.3=2.98m/s
Initial velocity U= 2.98m/s or 10.73km/h (Using the conversion rate 36km/h=10m/s)